The present invention relates to a fixed type constant velocity joint used in power transmission systems for automobiles and various industrial machines and adapted to tolerate only an operating angular displacement between two shafts on the driving and driven sides, and it also relates to an assembling method therefor.
For example, there is a fixed type constant velocity joint in the form of a UF (undercut free) type shown in FIG. 15. This constant velocity joint comprises an outer ring 5 that has a mouth portion 4 and whose inner spherical surface 1 is formed with a plurality of track grooves 2 disposed at circumferentially equispaced intervals to extend axially toward an open end 3, an inner ring 8 whose outer spherical surface 6 is formed with a plurality of track grooves 7 paired with the track grooves 2 of the outer ring 5 and disposed at circumferentially equispaced intervals to extend axially, a plurality of balls 9 interposed between the track grooves 2 and 7 of the outer and inner rings 5 and 8 for torque transmission, and a cage 10 interposed between the inner spherical surface 1 of the outer ring 5 and the outer spherical surface 6 of the inner ring 8 for holding the balls 9. The plurality of balls 9 are received in pockets 13 formed in the cage 10 and disposed at circumferentially equispaced intervals.
A stem portion (not shown) integrally extending from the mouth portion 4 of the outer ring 5 has, for example, a rotatable shaft on the driven side connected thereto, while the inner ring 8 has a rotatable shaft on the driving side joined thereto as by serrations. This results in a construction that allows torque transmission while tolerating operating angular displacement between the two rotatable shafts.
FIG. 15 shows the state in which the operating angle xcex8 is 0xc2x0 and FIG. 16 shows the state in which the operating angle xcex8 is at its maximum (50xc2x0). The operating angle xcex8 shall mean an angle formed between the rotatable shaft X of the outer ring 5 and the rotatable shaft Y of the inner ring 8. Further, when the rotatable shafts X and Y of the outer and inner rings 5 and 8 take an operating angle xcex8 other than 0xc2x0, the plane perpendicular to the bisector of the angle xcex8 between the two rotatable shafts X and Y is referred to as the joint center plane Pxe2x80x2. If all of the balls 9 are in the joint center plane P when an operating angle xcex8 is taken, the distances from the ball center to the two rotatable axes X and Y are equal; therefore, transmission of rotary motion at constant velocity is performed between the two rotatable shafts X and Y. The intersection between the joint center plane Pxe2x80x2 and the rotatable shaft X, Y is referred to as the joint center Oxe2x80x2. In this constant velocity joint, the joint center Oxe2x80x2 is fixed without regard to the operating angle xcex8.
Each track groove 2 in the outer ring 5 is formed to predetermined depths from the inner spherical surface 1 of the outer ring 5, its depth gradually varying axially. This track groove 2 has an arcuate bottom 2a in the innermost region of the mouth portion 4, and a straight bottom 2b parallel to the rotatable shaft X on the open side of the mouth portion 4. Each track groove 7 of the inner ring 8 is formed to predetermined depths from the outer spherical surface 6 of the inner ring 8, its depth gradually varying axially. This track groove 7 has an arcuate bottom 7a on the open side of the mouth portion 4, and a straight bottom 7b parallel to the rotatable shaft Y in the innermost region of the mouth portion 4.
In recent years, there have been needs for reduction of the minimum radius of rotation of automobiles (particularly, light-weight cars and small-sized cars) and the increase of the operating angle as the degree of freedom of geometrical design is increased for better automobile steerability. However, with conventional constant velocity joints, an operating angle xcex8 max=50xc2x0 is the upper limit. And realizing the increase of the operating angle requires increasing the outer diameter of the mouth portion 4 of the outer ring 5. Therefore, at present a design that is counter to light weight and compact design cannot but be resorted to.
In this constant velocity joint, in order to provide a construction capable of taking large operating angles, the center of curvature, O1xe2x80x2, of the track groove 2 of the outer ring 5 is axially offset by an distance Fxe2x80x2 with respect to the center of curvature, O4xe2x80x2, of the inner spherical surface 1 of the outer ring 5, that is the outer spherical surface 12 of the cage 10, and the center of curvature, O2xe2x80x2, of the track groove 7 of the inner ring 8 is axially offset by an distance Fxe2x80x2 in axially opposite directions of the outer ring-side with respect to the center of curvature, O3xe2x80x2, of the outer spherical surface 6 of the inner ring 8, that is the inner spherical surface 11 of the cage 10 (track offset). Similarly, the center of curvature, O3xe2x80x2, of the inner spherical surface 11 of the cage 10 and the center of curvature, O4xe2x80x2, of the outer spherical surface 12 are axially offset with respect to the joint center plane Pxe2x80x2 in opposite directions by an equal distance fxe2x80x2 (cage offset).
As a result, a pair of track grooves 2 and 7 form a wedge-shaped track whose spacing gradually varies axially in one direction. Each ball 9 is rollably incorporated between a pair of track grooves 2 and 7 and is subjected to the action of an axial tension that causes the ball to move toward wider spacings in the wedge-shaped track when torque is transmitted with the outer and inner rings 5 and 8 taking an operating angle xcex8.
Further, in this constant velocity joint, the ratio of the cage offset quantity fxe2x80x2 to the total offset quantity (fxe2x80x2+Fxe2x80x2) (the sum of the cage offset quantity fxe2x80x2 and the track offset quantity Fxe2x80x2) is set such that fxe2x80x2/(fxe2x80x2+Fxe2x80x2)=0-0.11. Since optimum ranges of the cage offset quantity fxe2x80x2 and the total offset quantity (fxe2x80x2+Fxe2x80x2) vary according to the size of the joint, they have to be determined in relation to the fundamental size indicating the joint size.
Therefore, the ratio, fxe2x80x2/PCRxe2x80x2, of the cage offset quantity fxe2x80x2 to the length PCRxe2x80x2 of a line connecting the center of curvature, O2xe2x80x2, of the track groove 7 of the inner ring 8 (or the center of curvature, O1xe2x80x2, of the track groove 2 of the outer ring 5) and the center of the ball 9, is used, and, in conventional cases, the optimum range of the cage offset quantity fxe2x80x2 is so set as to satisfy the relation fxe2x80x2/PCRxe2x80x2=0-0.017. Further, the ratio of the cage offset quantity fxe2x80x2 to the total offset quantity (fxe2x80x2+Fxe2x80x2) is so set as to satisfy the following conditions:
when (fxe2x80x2+Fxe2x80x2)/PCRxe2x80x2=0.14, fxe2x80x2/(fxe2x80x2+Fxe2x80x2)=0,
and
when (fxe2x80x2+Fxe2x80x2)/PCRxe2x80x2=0.15, fxe2x80x2/(fxe2x80x2+Fxe2x80x2)=0.11.
In this connection, the conventional constant velocity joint has been designed to have a size and shape that satisfy the conditions that include fxe2x80x2/(fxe2x80x2+Fxe2x80x2)=0-0.11 and fxe2x80x2/PCRxe2x80x2=0-0.017. Therefore, the joint-making assembling of the inner ring 8, cage 10 and outer ring 5 has been performed in the following manner.
In incorporating the inner ring 8 into the cage 10, the inner ring 8 is positioned relative to the cage 10 at right angles to the axis of the cage 10, as shown in FIG. 17, and the spherical projection 14 positioned between the track grooves 7 of the inner ring 8 is dropped into one of the pockets 13 of the cage 10; in this state, the inner ring 8 is inserted into the cage 10. When the center O5xe2x80x2 of the inner ring 8 coincides with the center O6xe2x80x2 of the cage 10, the inner ring 8 is turned in a right angle direction with respect to the axis of the cage 10 and disposed in the normal position.
Further, in incorporating the cage 10 into the outer ring 5, the cage 10 is positioned at right angles with the outer ring 5, as shown in FIG. 18, and the spherical projection 15 positioned between the track grooves 2 of the outer ring 5 is aligned with a pocket 13 of the cage 10 and inserted therein. When the center O6xe2x80x2 of the cage 10 coincides with the spherical center O7xe2x80x2 of the outer ring 5, the cage 10 is turned in a right angle direction with respect to the outer ring 5 and disposed in the normal position.
In the cage 10, in order to avoid interference with the spherical projections 14 during the incorporation of the inner ring 8, interference with spherical projections 15 during the incorporation into the outer ring 5, and interference that, when an operating angle is taken during the incorporation of balls 9, is caused by the peripheral movement of other balls 9, it is necessary that the peripheral dimension of the pockets 13 be set at the proper value.
Increasing the peripheral dimension of the pockets 13 suppresses the interference that occurs during the incorporation but lowers the strength of the cage 10 since the pillar width between adjacent pockets 13 is reduced. Reversely, reducing the peripheral dimension of the pockets 13 increases the pillar width between adjacent pockets 13 and hence improves the strength of the cage 10 but makes it difficult to suppress the interference that occurs during incorporation.
Therefore, the peripheral dimension of the pockets 13 has to be set with consideration given to the cage strength to avoid interference between the spherical projections 14 and 15 of the inner and outer rings 8 and 5 and interference due to peripheral movement of the balls 9; thus, there have been many limitations on the design of the joint.
Depending on the joint size and offset quantity, the pillar width dimension between adjacent pockets 13 is reduced to lower the cage strength in some cases; therefore, countermeasures have been taken by providing a pair of incorporation-exclusive elongated openings at diametrically opposite positions in the cage 10 or forming a notch 16 (see FIGS. 15 and 17) in the inlet-side end edge of the spherical projection 14 of the inner ring 8 so as to facilitate the dropping of the cage 10 into the pocket 13. However, in this case, the cage 10 and inner ring 8 have to be machined, leading to an increase in cost.
During the incorporation of the inner ring 8 into the cage 10, the inner ring 8 has to be once dropped into the pocket 13 of the cage 10 and during the incorporation of the cage 10 into the outer ring 5 two-stage operation, i.e., inserting the cage 10 into the outer ring 5 and then turning it in the right angle direction, has to be performed. This has complicated automatic assembly, etc. in respective incorporating operations.
Further, since the conventional constant velocity joint is designed with a size and shape such that the ratio of the cage offset quantity fxe2x80x2 to the total offset quantity (fxe2x80x2+Fxe2x80x2) satisfies the above-mentioned conditions, the incorporation of the balls 9 has been performed in the following manner.
First, with the inner ring 8 and cage 10 incorporated into the outer ring 5, the track groove 2 of the outer ring 5, the pocket 13 of the cage 10, and the track groove 7 of the inner ring 8 are radially positioned relative to each other, as shown in FIG. 19, whereupon the cage 10 and inner ring 8 are axially tilted with respect to the outer ring 5 such that the clearance between the open end 3 of the outer ring 5 and the inlet-side end of the pocket 13 of the cage 10 is larger than the ball diameter.
One of the pockets 13 of the cage 10 thus faces the outside through the open end 3 of the outer ring 5 and the ball 9 is inserted through the clearance between the open end 3 of the outer ring 5 and the inlet-side end of the pocket 13 of the cage 10; in this manner, the balls 9 are successively inserted into the remaining pockets 13.
And, in incorporating the last ball 9, the latter is inserted into the pocket 13 in a phase with an incorporation angle xcfx86=0xc2x0, as shown in FIG. 20, that is, in a direction that coincides with the direction connecting the center of the pocket 13 and the center of the cage 10.
In inserting the last ball 9, the balls 9 that are on the track side having an axial curvature in the innermost region of the outer ring 5, that is, the balls 9 in xcfx86=120xc2x0 and 240xc2x0 phases, move peripherally and interfere with the ends of the pockets 13, which movement is caused by axially tilting the cage 10 with respect to the outer ring 5. If the peripheral dimension of the pockets 13 is increased, interference during incorporation can be suppressed, but the width dimension of the pillar 14 between adjacent pockets 13 becomes smaller and hence the strength of the cage 10 lowers. Reversely, if the peripheral dimension of the pockets 13 is reduced, the width dimension of the pillars 14 of the cage 10 can be increased, so that the strength of the cage 10 can be improved; however, it becomes difficult to suppress interference during incorporation.
Therefore, the peripheral dimension of the pockets 13 has to be set with consideration given to the cage strength to avoid interference due to the peripheral movement of other balls 9 when an operating angle is taken during the incorporation of the ball 9. Thus there have been needs for the absence of interference due to the peripheral movement of balls 9 and for easily increasing the strength of the cage 10.
An object of the present invention is to easily realize the increase of the maximum operating angle, to suppress interference during the incorporation of parts, to simplify the incorporating operation, and to easily realize the increase of the strength of the cage.
According to the invention, in a fixed type constant velocity joint comprising an outer ring whose inner spherical surface is formed with a plurality of track grooves disposed at circumferentially equispaced intervals to extend axially toward the open end, an inner ring whose outer spherical surface is formed with a plurality of track grooves paired with said track grooves of the outer ring and disposed at circumferentially equispaced intervals to extend axially, a plurality of balls interposed between the track grooves of the outer and inner rings to transmit torque, and a cage interposed between the inner spherical surface of the outer ring and outer spherical surface of the inner ring to hold the balls, the open-side groove bottoms of the track grooves of the outer ring are tapered to be linearly diameter-expanded toward the open end thereof.
In addition, the innermost-side groove bottom of each track groove of the inner ring is shaped as a taper linearly diameter-expanded toward the innermost region. Further, it is desirable that the open-side groove bottoms of the track grooves of said outer ring or the innermost-side groove bottoms of the track grooves of the inner ring are tapered so that they are at right angles with a line connecting the center of curvature of the track groove of the outer ring (or the center of curvature of the track groove of the inner ring) and the ball center.
As a result, in the invention, the operating angle formed between the rotatable shafts of the outer and inner rings can be increased to a maximum of 52xc2x0, easily realizing the increase of the operating angle without increasing the outer diameter of the outer ring, the compact size of the outer ring, and the increase of the load capacity, and the needs for increased functionality and workability can be quickly coped with.
In the constant velocity joint of the invention, it is desirable that the centers of the outer and inner peripheral surfaces of the cage be axially offset with respect to the joint center plane including the ball center in opposite directions by an equal distance and that the cage offset quantity be set at a large value so as to ensure that the pockets of the cage restrain the balls from jumping out of the open end of the outer ring.
Setting the cage offset quantity at a large value has the advantage of being capable of increasing the wall-thickness of the inlet side of the cage, into which the inner ring is to be incorporated, to increase the strength. Further, since the wall-thickness of the inlet side of the cage can be increased, it is possible for the pocket of the cage to restrain the ball form jumping out of the open end of the outer ring when an operating angle is taken.
However, if the cage offset quantity is too large, {circle around (1)} the amount of peripheral movement of the ball in the pocket of the cage is increased, producing the necessity of increasing the peripheral dimension of the pocket in order to secure the proper movement of the ball, leading to the thinning of the pillar of the cage, posing a problem in an aspect of strength. {circle around (2)} The wall-thickness of the innermost region located opposite to the inlet side of the cage is reduced, posing a problem in an aspect of strength.
It follows from the above that excessive cage offset quantity is not desirable and that there exists the optimum range capable of keeping balance between the significance of providing the cage offset quantity and the problems {circle around (1)} and {circle around (2)}. Since the optimum range of cage offset quantity varies with the size of the joint, it has to be determined in relation to the fundamental size indicating the size of the joint. Therefore, the ratio (f/PCR) of the cage offset quantity f to the length PCR of a line connecting the center of curvature of the track groove of the outer ring (or the center of curvature of the track groove of the inner ring) and the ball center is used.
The cage offset quantity f in the invention is set such that the ratio (f/PCR) of the cage offset quantity f to the length PCR of a line connecting the center of curvature of the track groove of the outer ring (or the center of curvature of the track groove of the inner ring) and the ball center is within the range of 0.017-0.150.
If this ratio (f/PCR) is larger than 0.150, the problems {circle around (1)} and {circle around (2)} arise, and, inversely, if it is smaller than 0.017, the significance of providing the cage offset quantity f is lost. That is, the purpose of the cage offset is to prevent the point of contact of the ball with the open side of the outer ring from sticking out of the pocket of the cage; with the range of smaller than 0.017, the purpose cannot be attained. Therefore, from the standpoint of securing cage strength and durability, the optimum range of cage offset quantity f is such that the ratio (f/PCR) is within the range of 0.017-0.150.
In the invention, besides the cage offset quantity f described above, the center of curvature of the track groove of the outer ring and the center of curvature of the track groove of the inner ring are axially offset with respect to the joint center plane including the ball center in opposite directions by an equal distance, and the track offset quantity F is so set between it and the cage offset quantity f as to satisfy the condition f/(f+F) =0.12-1.0.
This suppresses interference between members during the incorporation of the inner ring, cage, and outer ring to simplify the incorporating operation, and lessens the limitations on the design of the joint, making it possible to easily secure the strength of the cage.
That is, since the opening diameter of the innermost region of the cage becomes larger than in the conventional type, in incorporating the inner ring into the cage, the inner ring can be inserted into the cage without dropping the spherical projection of the inner ring into the pocket of the cage from the innermost region of the cage. Further, since the opening diameter of the outer ring becomes larger than in the conventional type, in incorporating the cage into the outer ring, the cage can be inserted into the outer ring with the cage facing the same axial direction and with the pocket aligned with the spherical projection of the outer ring.
As a result, the peripheral dimension of the pocket can be set by only giving consideration to the amount of peripheral movement of the ball when an operating angle is taken during the incorporation of the ball, without having to give consideration to interference with the spherical projection during the incorporation of the inner ring and interference with the spherical projection during incorporation into the outer ring; thus, the design of the joint is facilitated.
In the relation between the track offset quantity F and the cage offset quantity f, when (f+F) is larger than 1.0, that is, when the track offset quantity F becomes minus, the direction of offset is reversed, providing a construction in which contact position sticks out of the pocket in the phase where the innermost region of the cage is loaded; thus, this does not establish a mechanism. Reversely, if it is smaller than 0.12, the resulting range is the same as that employed by the conventional constant velocity joint and is insufficient to provide a mechanism for increased operating angles based on this constant velocity joint. Therefore, from the standpoint of mechanism establishment, most suitably f/(f+F) is within the range of 0.12-1.0.
In the invention, in the relation of the track offset quantity F, the cage offset quantity f, and length PCR of a line connecting the center of curvature of the track groove of the outer ring (or the center of curvature of the track groove of the inner ring) and the center of the ball, the following conditions are satisfied;
when (f+F)/PCR=0.1, f/(f+F)=0.35 or above,
when (f+F)/PCR=0.2, f/(f+F)=0.11 or above,
and
when (f+F)/PCR=0.3, f/(f+F)=0.03 or above.
This setting of the conditions realizes the increase of the maximum operating angle.
In realizing the increase of the maximum operating angle, the method of assembling a constant velocity joint adapted to satisfy said conditions involves, when the last ball is to be incorporated into a pocket of the cage, inserting the ball in the direction that forms a predetermined phase angle with the radial direction of the cage passing through the center of the pocket. This allows the interference angle between the already incorporated ball in the innermost region of the outer ring and the pillar between adjacent cage pockets to be made larger than in the conventional case.
Therefore, during the insertion of the last ball, the amount of peripheral movement of the ball on the track side having a curvature axially of the innermost region of the outer ring becomes smaller than in the conventional case, so that the pillar width dimension between adjacent pockets can be set at a large value, facilitating the increase of the strength of the cage.
During the incorporation of balls, there is no possibility of a ball being positioned diametrically opposite to the ball insertion side concerning the radial direction of the cage, so that a substantial axial length of the track grooves becomes unnecessary, with the result that the axial length of the outer ring can be reduced to make the entire assembly compact in size.
If the open end of the inner spherical surface of the outer ring is chamfered or if, in each pocket of the cage, the outside open edges of the axially opposed side surfaces are chamfered, then the insertion into the outer ring can be further facilitated in such a manner that with the cage facing the same axial direction, the pocket is aligned with the spherical projection of the outer ring.
Further, the use of eight balls makes it possible to reduce the load on a single ball and to increase efficiency and provides superiority in strength, loading torque, and durability, allowing the ball diameter to be reduced, so that the entire joint can be reduced in size.
Further, it is desirable that a pocket clearance be formed so as not to retrain the ball in the innermost region of the pocket of the cage. This allows the strength of the cage to be secured even if the wall-thickness of the innermost region of the cage is reduced with the increase of the cage offset quantity.